The objective of advanced surveillance systems is not only to collect as much sensor data as possible, but also to process and represent it in a meaningful way for supporting situation awareness of a decision maker. However, in today's surveillance systems, there is still a need for information processing methods that meet these higher-level objectives. In this article, the information flow inside of an advanced surveillance system is highlighted and the term situation is discussed with respect to different abstraction levels. Furthermore, several challenges are identified that an advanced system has to address. Therefore, methods selected for information processing should meet these challenges in order to provide a high-level functionality for situation awareness support.